Process for the production of magnetic materials



FIELD srxzuam, m osxsreus TAKAAKI YAMAMOTO ETAL H, m osksrzfis H T 6 N ER T 5 D L E F PROCESS FOR THE PRODUCTION OF MAGNETIC MATERIALS BY THEUTILIZATION OF MAGNETIC ANNEALING EFFECT .100 no 5001mm saw/m sun PER:can N: m IRON 7 836 E m fi 55 2529 2 FREQUENCY, F, IN CYCLES PER SECONDMarch 17,

Filed Feb. 8, 1965 PER CENT N! [N J'RON v r March 1964v TAKAAKI YAMAMOTOETAL 7 PROCESS FOR THE PRODUCTION OF MAGNETIC MATERIALS BY THEUTILIZATION OF MAGNETIC ANNEALING EFFECT Filed Feb. 8, 1965 2Sheets-Sheet 2 magnetic field app smaH air gap perpendicular during heaTTreafmenf j \ongifud'mai direcTion f The Tape magnefizing coil elecTricfurnace 0000 nno'nnonnn noo o Toroidal specimen I cylindncal yoreINVENTOILS Mad-4.44)

United States Patent PROCESS FOR THE PRODUCTION OF MAGNETIC MATERIALS BYTHE UTILIZATION OF MAG- NETIC ANNEALING EFFECT Takaaki Yamamoto, 6643Kugenuma, Fujisawa-eity,

Kanagawa-ken, Japan; Yutaka Nakamura, 1001 Yukigaya-cho, Ota-ku, Tokyo,Japan; and Tomio Nagaghima, 14, 3-ch0me, Nishimizue, Edogawa-kn, Tokyo,

apan

Filed Feb. 8, 1963, Ser. No. 257,210 1 Claim. (Cl. 148-108) The presentinvention relates to a process of production of magnetic materials withthe constancy of permeability by the utilization of a magnetic annealingeffect, wherein a ferromagnetic metallic tape wound to form a toroid isannealed in a magnetic field applied perpendicularly to the longitudinaldirection of the tape and further, wherein a small air gap, whichinduces a weak demagnetizing field in the longitudinal direction of thetape, is provided in the magnetic path of the toroidal core, and alsothe temperature and time of the heat treatment for the tape are adjustedsuch as to have almost zero crystal magnetic anisotropy of cubicsymmetry and at the same time to induce uniaxial anisotropyperpendicularly to the longitudinal direction of the tape.

This is a continuation-in-part application of the copending applicationSerial No. 13,550, filed March 8, 1960, now abandoned.

It is the main object of the present invention to provide a process ofproduction of magnetic materials, which have the property of constancyof permeability to a relatively high magnetic field strength in thelongitudinal direction of the tape, which also have a very smallhysteresis loss and which further have only a slight change in the valueof the permeability to a relatively high frequency.

Heretofore, as materials with the constancy of permeability, there areknown Perminvar (Bell Telephone Lab.) utilized with Perminvarcharacteristics, Isoperm (Allgemeine Elektrizitats Gesellschaft)utilized with a rolling magnetic anisotropy and magnetic powderscompressed with a binder. However, the initial permeability of Perminvarremains constant at about =400 up to an order of 4 Oe., but it has thedisadvantage that when a large magnetic field is applied thereto, theconstancy of permeability will be nearly lost. The permeability of theIsoperm is low (about 100) and the hysteresis loss is high. Further, thematerial utilized with the magnetic powder can only be produced to havethe permeability of an order of 100-300.

It is another object of the present invention to provide a process ofproduction of magnetic materials, wherein the magnetic materials havethe permeability of about 1200-1500 and the frequency dependence ofpermeability is almost constant to about 50 kc., and also even afterapplying a large magnetic field enough to saturate the magnetic fluxdensity, the property of the constancy of permeability remains. Themagnetic instability S I' B r Ma is only to be of the order of 0.10.6%,wherein is the initial permeability and pr is the reversiblepermeability at the point of residual magnetization.

In case of cooling a magnetic material from a high temperature in amagnetic field, when the material eX- hibits magnetic annealing, it iswell known that the direction of the magnetization vector in eachmagnetic domain is fixed at the same direction, as that of a magneticfield applied at a high temperature.

When the material is treated by heat in a magnetic field, theoreticallythe magnetization process in the direction 3,l25,472 Patented Mar. 17,1964 "ice siderably improved. However, in a ferromagnetic alloy,

the crystal anisotropy of cubic symmetry is usually superior over or ofthe same order as the uniaxial anisotropy constant induced by coolingfrom a high temperature in the magnetic field, and consequently theconstancy of permeability is harmed. Accordingly, materials in which thecrystal anisotropy constant is originally small in comparison with theuniaxial anisotropy constant or materials realized of such property by aheat-treatment are suitable for this purpose. In order to obtain highpermeability, the uniaxial anisotropy constant is preferably small inthe limitation permissible, however, in case no demagnetizing field inthe direction of magnetization is available, but a demagnetizing fieldin the vertical direction is present, it is difficult to fix completelythe magnetization vector in the vertical direction, and this is apparentfrom the relation between a dimensional ratio of the rod specimen andthe The above Table 1 shows values obtained from the difference of themagnetization curves when polycrystal rod specimens of 60% Ni40% Fe and65% Ni35% Fe, respectively, are cooled from 550 C. to 250 C. at thecooling rate of 10 C./hr. in a magnetic field disposed parallelly to therod axis or in a circular magnetic field disposed perpendicularly to therod axis. Further, a dimensional ratio in the Table 1 discloses thelength of the long axis in relation to the length of the short axis, andK shows the uniaxial anisotropy constant in ergs/cm. Magnitudes of theuniaxial anisotropy constant are the aim of the magnetic annealingeffect. Accordingly, from the result of the Table l, in case of windinga tape in form of a toroid, a suitable demagnetizing field in thedirection of magnetization can be achieved to obtain the samecharacteristic as rod specimens and also this demagnetizing field can bemade by providing a suitable air gap in the magnetic circuit.

Now, the process of production of magnetic materials according to thepresent invention will be described more definitely with reference toworking Examples 1 to 3.

Example 1 A binary alloy composed of the composition of 60% Ni and 40%Fe is worked into a tape having a thickness of 0.03 mm. by cold rolling,and this alloy tape is wound in the form of a toroid, while insulatingwith magnesia powder of 500 mesh per/cm. between the layers of the tapeand a demagnetizing field is arranged by providing an air gap ofabout0.05 mm. in the magnetic circuit, which is brought about by cuttingout a thin portion across the toroid. Then, the wound tape is annealedin an atmosphere of dry hydrogen at about 1200 C. for 3 hours, so as toraise the purity of the material and to remove the mechanical stress.Then, the tape of toroid form is clamped from both sides thereof bycylindrical yokes of pure iron, so as not to produce any distortion, andconsequently a demagnetizing field in the axial direction of the toroidis obtained, and while applying a magnetic field of about 30 e. in theaxial direction of the wound tape from the outside, the Wound tape isslowly cooled at the coolingrate of C./hr. in an atmosphere of dryhydrogen from 500 C. to 270 C.

Example 2 A ternary alloy composed of the composition of 60% Ni, 40% Feand an addition of 1% Mn is worked by cold rolling, so as to produce atape having a thickness of 0.02 mm. and this tape is cut to obtain alength of about cm. and is wound to form a toroid, while insulating withmagnesia powder 500 mesh per/cm. between the layers of the tape. Then,firstly the Wound tape is annealed in the atmosphere of dry hydrogen atabout 1000 C. for 5 hours, so as to raise the purity of the Wound tapeand to remove the mechanical stress. Thereafter, ten of the toroidaltapes are juxtaposed, so as to obtain a demagnetizing field in the axialdirection thereof, and while applying a magnetic field of about 30 Oe.to the sample from the outside, the sample is slowly cooled at a coolingrate of 10 C./hr. in an atmosphere of dry hydrogen from 550 C. to 280 C.

Example 3 A ternary alloy composed of the composition of 65% Ni, 35% Feand an addition of 0.5% Mn is worked to produce a tape of a thickness of0.05 mm., and after this tape is Wound to form a toroid, an air gap ofabout 0.05 mm. is formed in the magnetic circuit, Which is brought aboutby cutting a thin layer across the wound tape. Then, firstly the woundtape is annealed at 1100 C. for 3 hours in an atmosphere of dry hydrogenso as to raise the purity of the tape and to remove any mechanicalstress. Thereafter, while applying a magnetic field of about Oe. in thesame procedure as that in the working Example 1, the tape is slowlycooled at a cooling rate of 40 C./hr. in the atmosphere of dry hydrogenfrom 500 C. to 250 C.

Table 2 discloses now the magnetic characteristics together with theconditions of the heat treatment in the Examples 1 to 3.

FIG. 5 is a curve depicting the ratio of residual magnetic flux densitywith the percentage of nickel in iron;

FIG. 6 is a curve depicting the uniaxial anisotropy constant with thepercentage of nickel in iron;

FIG. 7 is a perspective view of a wound tape indicating the air gap;

FIG. 8 is a schematic axial section of an electric furnace; and

FIG. 9 is an end view of a wound tape disclosing the relationshipbetween the length of the tape and the air gap.

Referring now to the drawings, and in particular to FIG. 1, in thisfigure the ordinate indicates the. magnetic flux density B and theabscissa indicates the strength H (0a.) of the magnetic field.

In FIG. 2 the ordinate indicates the permeability ,u. and

the abscissa indicates the frequency in cycles, s./sec., and the markindicates ,u. for an amplitude of 0.45 Oe., and

the mark indicates a permeability a and the abscissa indicates thestrength H (Oe.) of a magnetic field.

The values of the permeability obtained by the present invention, asapparent from FIGS 1 to 3 and the Table 2, are attained at a value of1200-1500 up to an order or 445 Oe. and also the frequencycharacteristic shows only a slight reduction of permeability up to anorder of about kc, and this fact shows that it is usable as a materialwith the constancy of permeability to the range of frequency of an orderof 50 kc. hysteresis loss is a part of an advantageous condition forusing it at an audible frequency, for instance, a hysteresis loss forthe present material in 5000 gauss of magnetic flux densityis 140-240ergs/cm. however, this is only a value of /6 A of the loss encounteredin the use of Perminvar.

The basis of the selection of the composition, temperature and time ofheat treatment will now be more clearly set forth:

In connection with Permalloy (Fe-Ni) it is known, that a crystalmagnetic anisotropy of cubic symmetry is changed with the formation of asuperlattice structure. Further, a degree of the order in Permalloy isconsider- TABLE 2 Working example 1 2 3 Comlposition by weight):

2/100 5/100. Condition of demagnetizing field Wound the tape air gap.

of length of 10 cm. Stress rcmovinghigh temperature treatment:

Temperature C.) 1,200 1,000 1,100. Time (ha) 3 i 4. Magnetic annealingcondition:

Magnetic field Perpendicular Perpendicular Perpendicular magnetic fieldmagnetic field magnetic field 30 0e. cylindri- 30 0a., 10 of 20 0e.cylindrical yoke. samples are laid cal yoke.

in parallel. Temperature range applied field C.) 500-270 550280 600-250.

Cooling rate C.[hr 5 O./hr 10 O./hr 40 O./hr. Permeability (H):

Static character 1,220 (to 4 2 Oe.) 1,500 (to 3.8 Oe.) 1,120 (to 4.50e.) 10 kc. (0.8 00.) Amplitude. 1,170 l,460 1,060. 30 kc. (0.8 0e.)Amplitude. 980 1,270 850. Hysteresis loss erg/cmfi/cycle (Bm=5,000gauss). 140" 240 180. Cocrsive force (Oc.) 0.06.-. 0.1 0.05. Residualflux density (gauss) 120 200 150. Instability (percent) 0.1 0.6 0.3.

With the above stated and other objects in view, which will becomeapparent in the following detailed description, the present inventionwill be clearly understood in connection With the accompanying drawings,in which:

FIGS. 1, 2 and. 3 are, respectively, hysterisis curves, frequencycharacteristics and magnetic field strength permeability curves;

FIG. 4 is a curve depicting the crystal anisotropy constant with thepercentage of nickel in iron;

ably effected by the cooling rate in a temperature range of about 600 C.to 300 C.

FIG. 4 discloses values measured by a torque meter at room temperature acrystal anisotropy constant K of cubic symmetry, respectively, when thealloys with various compositions are cooled at the cooling rate ofC./hr., 55 C./hr., and 25 C./l1r. in a temperature range of 600 'C. (seeR. M. Bozor-th and J. G. Walker; Phys. Rev. 89 (1953), 624). In FIG. 4,the ordinate depicts an Further, the smallness of anistropy constant inergs/crn. and the abscissa depicts the content of Ni by wt. percent. Thevalues upon adopting 105 C./hr., are shown by full lines with an X, thevalues upon adopting 55 C./hr. are shown by dotted lines, and thevalues, upon adopting 25 C./hr., are shown by full lines with an 0. Asseen from the drawings, the composition of the crystal anisotropy Kgoing down to zero is about 75% Ni upon adopting the cooling rate of 105C./hr., 67% Ni upon adopting 55 C./hr., and 63% Ni upon adopting 25C./hr. Accordingly, it is seen that the composition of the substance, inwhich crystal anisotropy moves to zero, together with the cooling rateis lowered, is shifted toward the smaller N1 content.

FIG. 5 shows values at the room temperature of the ratio of a residualfiux density Br to a magnetic flux density Bs at 100 Oe. measured afterpolycrystal rod specimens (0.5 mm. diameter and 150 cm. length) ofPermalloy of various compositions are treated at the cooling rates of 31OA C./hr. indicated in the drawing by A, 600 C./hr. by 100 C./hr. by anX, C./hr. by an O, and 1 C./hr. by a period between 600 C. to 250 C. ina magnetic field of about 0e. Br/Bs is a quantity sensible to crystalanisotropy of cubic symmetry and uniaxial anisotropy induced by thecooling in the magnetic field. Generally, the smaller the crystalanisotropy and also the larger uniaxial anisotropy, the larger getsBr/Bs. From the drawings, it can be determined that in a range of 50%70%of Ni content, this quantity is considerably varied with the coolingrates, and in order to increase the value of Br/Bs, it has been foundthat the smaller the content of Ni which is adopted, the smaller is thecooling rate necesary to be used.

On the other hand, the uniaxial anisotropy constant K also varies withthe cooling rate, and generally it is larger when the cooling rate islowered, however, it is known that when a degree of a long range orderof superlattice is developed above some degree, the uniaxial anisotropyis decreased inversely.

FIG. 6 discloses the result concerning the difference in the uniaxialanisotropy constant K in accordance with the compositions of thePermalloys. The value of K is obtained from the difference of the curvesof magnetization, when the polycrystal rod is cooled at a cooling rateof 10 C./hr. from 550 C. to 250 C. in the magnetic field parallel to therod axis and in the circular magnetic field perpendicular to the rodaxis. It can be easily determined from the drawing that the compositionof about 60% Ni has the largest value.

From the above result, in the range of the composition containing about5070% Ni, the uniaxial anisotropy K is relatively large and also thecrystal anisotropy constant can be made to zero or to a considerablysmall value by slowly cooling at a cooling rate of 100 C./hr. or atbelow the rate thereof. Further, Br/Bs aims to make K larger and Ksmaller. However, this ratio, in the range of 50%70% Ni, can be madelarger by cooling it slowly at the rate of 100 C./hr. or at slower rate.

It has already been described that by the use of a suitable heattreatment and time, crystal anisotropy constant must be made to zero orto a considerably small value, and also the uniaxial anisotropy constantis necessary to be made preferably of a larger value. This condition, asabove described, can be provided by a process according to which a tapeof an alloy composed of a material of 30%50% Fe by weight and 70%50% Niby weight is slowly cooled in a magnetic field at the rate of 100 C./hr.or at a smaller rate within a range of 600 C.200 C.

Referring now to FIG. 7 of the drawings, the formation of the air gap isdisclosed, which is provided to induce a weak demagnetizing field in thelongitudinal direction of the tape. It should be emphasized that the airgap is disposed perpendicularly to the winding direction of the toroid.

As clearly disclosed in FIG. 8 of the drawings, a wound tape is clampedbetween the ends of a cylindrical yoke and heated in an electricalfurnace by providing a vertical magnetic field in order to obtain thedesired characteristic.

As pointed out in the Table 1, the values of uniaxial anisotropy areconstant, when the length ratio is varied. The demagnetizing factor inthe toroidal core is preferably about 0.003.

As indicated in FIG. 9 of the drawings, the demagnetizing factor N isobtained by means of the length of the air gap, whereby l is an averagelength of the magnetic path in the toroidal core, as expressed in theformula Z1 N -41r l in which, for instance, l= 6- cm. and the air gap isobtained from the formula, namely 1:0.03 cm.

In this maner, the values can be determined and it has been set forthabove that the air gap can be 0.05 cm.

As above described, a tape of Permalloy (Fe-Ni) of a suitablecomposition and wound to form a toroid is applied in a magnetic fieldperpendicular to the longitudinal direction of the tape and is heattreated, and further by applying a weak demagnetizing field in thelongitudinal direction of the tape and by selecting suitably thetemperature and time for the heat treatment of the tape, materials withthe constancy of permeability having very superior characteristics, incomparison with the known various materials with the constancy ofpermeability can be produced by the present invention.

While We have disclosed several embodiments of the present invention, itis to be understood that these embodiments are given by example only andnot in a limiting sense, the scope of the present invention beingdetermined by the objects and the claim.

We claim:

A process of the production of a magnetic material having a constancy ofpermeability by the utilization of a magnetic annealing effect,comprising the steps of working an alloy composed of 30 to 50% Fe byweight,

70 to 50% Ni by weight, and 0 to 1% Mn by weight to a ferromagnetic tapewound to form a toroid and defining a plurality of layers, applyingmagnesia powder of 500 mesh per/cm. be-

tween each pair of adjacent layers of said tape and defining an air gapof about 0.05 mm. across said Wound tape in the magnetic path of saidtape,

annealing said tape in an atmosphere of dry hydrogen at about 1000 C. toabout 1200 C. for a time period of about 3 to 5 hours,

applying a magnetic field of up to about 30 Oe. in axial direction ofsaid wound tape, and

cooling said wound tape at a cooling rate of no more than C./hr. betweena temperature range of about 600 C. to 200 C. in a magnetic fielddisposed perpendicularly to the direction of magnetize,

whereby the crystal anisotropy constancy of the cubic symmetry isconsiderably reduced and the uniaxial anisotropy perpendicularly to thelongitudinal direction of said wound tape is induced simultaneously.

No references cited.

